Thanks to medical advances, we’re now having children later and later in life.
And it’s making many scientists fear for the future, discovers Jemima Lewis

These days, I dream that I am back in the early stages of my relationship with my now-husband, Henry. But instead of asking me to marry him, he is dumping me. I am back at square one: single, in my mid-thirties, and – this is the bit that makes me feel like I’m having a heart-attack – childless.

Biologically speaking, I was late to start a family: I had my first baby at 36, my second at 38 and my third at 40. It felt – still feels – like a piece of giddying good luck that I happened to meet a man I adored, with first-rate sperm, in the nick of time. Henry, the gallant knight, galloped me across the drawbridge of fertility before the portcullis clanged shut.

The realities of late-onset parenting, of course, are less of a fairy tale. Nor is there anything singular about our circumstances. In fact, we are part of a gathering demographic wave: one that some scientists and economists believe could have grave consequences for the world we live in.

The same thing is happening all over the globe. The age at which American women have their first babies has risen by four years since 1970, up to 25. In Japan – where adult incontinence pads now outsell nappies – it is 29.

Even in Africa, the birth rate among women under 20 has fallen by 20 per cent since the turn of the millennium.

But nowhere is the trend more pronounced than in Britain. The average age for a first-time mother in the UK has now hit 30 – meaning that we are delaying motherhood for longer than any other women in the world. Mothers in their early twenties are becoming increasingly rare, while those over 45 (just four years away from the average age of menopause) more than trebled between 2000 and 2011 – to 1,832, from a total of 723,913 live births.

This makes a lot of people very nervous. For one thing, women who start reproducing late tend to have smaller families, whether they like it or not. That means society is becoming increasingly top-heavy, with a dwindling supply of young people around to work, pay taxes and do the heavy lifting.

There are personal costs, too. Just because there seem to be lots of older mothers around, doesn’t mean it’s easily done. Those fossilised Hollywood actresses who pop out twins at an age when they should be collecting their free bus passes? They make it look easy – but they tend not to mention the donor eggs, or the surrogate wombs.

The Royal College of Obstetricians and Gynaecologists regularly puts out press statements which, though gently worded, suggest that its members would like to grab the women of Britain by the scruff of the neck and give us a jolly good shake. Wearily, they go over and over the numbers. Female fertility drops off steeply after the age of 35, while the risk of miscarriage goes rocketing up. Even with the help of IVF, a woman over 42 has only a five per cent chance of having a baby.

Birth defects are more common among the children of older women: everything from cleft palates to cerebral palsy. The risk that a pregnancy will yield a trisomy – a group of chromosomal abnormalities including Down’s syndrome – rises from two per cent when a women is in her twenties, to 30 per cent by the time she is in her forties.

And there’s something else. Though it is often portrayed as one, this isn’t just a female problem. Most men aren’t ready to settle down until somewhere around their mid-thirties. In an “information economy” like ours, people tend to stay in education longer to maximise their chances of getting a decent job. This is one of the major factors behind Britain’s declining birth rate: both men and women are more likely to go to university, which means they start work later, and take longer to feel established enough, financially and professionally, to start a family.

Nearly two-thirds of babies are now born to men over 30. And this, too, has consequences for the nation’s health. As evidenced by sixtysomething fathers like Rod Stewart and Michael Douglas, men keep producing new sperm all their lives. The older they get, the more likely they are to make a faulty batch. Neonatologists have long suspected that there may be a link between older fathers and a variety of birth defects, from dwarfism to dyslexia.

But recent research has made the connection much clearer. Last year, a study by geneticists in Iceland found that men pass on more genetic mutations to their children as they get older – and that these mutations might give rise to serious neurological disorders such as schizophrenia and autism. They concluded that a 40-year-old man was twice as likely as a 20 year-old to father a schizophrenic child. (It should be stressed, however, that the risk is still tiny, at less than one per cent.)

Environmental factors, too, can affect the quality of sperm. Dr Avi Reichenberg, a psychiatrist at King’s College, London, is one of the scientists leading research into epigenetics: a relatively new field exploring how genes are affected by factors other than the underlying DNA sequence.

What we eat and drink, whether we smoke, how stressed we get: all of these can change the way sperm cells behave. Older parents are generally more conscientious about living healthily, but for some the damage is already done. Years of absorbing airborne pollution, pesticides and all manner of endocrine disrupters may create “epimutations” in sperm cells, with consequences for the resulting children.

“Many children born to old fathers or old mothers develop normally,” Dr Reichenberg told me soothingly. But, “what the research shows is that the proportion of children of older fathers or mothers who have psychiatric or neurological disorders is higher than in children of parents of average age.” It sounds alarming. Of course it does. But as Reichenberg points out, there is a more optimistic way to look at it: “The risk has always been there. It’s only now that we are starting to understand it.”

This is an important point to make. Couples have always had children in their thirties and forties. Before the invention of the pill, there wasn’t much they could do to prevent it. Government records show that, for the first half of the 20th century, the number of babies born to women over 40 was actually much the same as it now. In fact, there was a tremendous surge in later-life pregnancies after the Second World War, when couples who had been separated by the fighting were finally reunited under the sheets. In fact, there were more babies born to women over 40 in 1947 than there were in 2011. (A whopping 34,696, compared with 29,350.)

The resulting generation of children – the Baby Boomers – were not disastrously compromised by learning disabilities, autism and the like (although it is impossible to compare the figures for then and now because such things were seldom diagnosed). In any case, the sky did not fall in. British society survived this epidemic of late-born babies, and prospered.

The idea that it is unusual, even unnatural, for a woman over 35 to procreate is a thoroughly modern prejudice – a consequence, in fact, of our space-age ability to manipulate nature. From the mid-Sixties onwards – after the contraceptive pill became available on the NHS – the number of babies born to women over 40 plummeted. By 1977, it had fallen to a meagre 5,988. Older mothers virtually disappeared from sight.

From a purely medical point of view, that might have been a good thing. But the world changed again. Like it or not (and I do) feminism happened. Most women now expect – and need – to work. So we don’t have much choice but to take a gamble, and hope that our ovaries will hold out.

The stakes, I grant you, are painfully high. Almost every woman who has tried to have a baby in her late thirties or early forties will have some kind of sorrowful tale to tell. As well as my three healthy babies, I had two miscarriages – one of them, at 12 weeks, quite dramatic. My husband came home from work to find me passed out on the bathroom floor in a pool of blood, like a murder victim in a Victorian penny dreadful.

That was an unhappy experience. I had been so excited about having another baby (it would have been my second), and when it fell out I felt that my body had failed it, and me. It was my own fault for being too old: I had played Russian roulette with my fertility, and lost. But as any gambler knows, you quickly forget about the losses once you start to win. Now that I have two more children, and my family is complete, I feel almost embarrassed by my good fortune.

People I love have suffered stillbirths, late miscarriages, infant deaths. Some have undergone many gruelling rounds of IVF without ever managing to conceive. Two of my friends did manage to get pregnant in their forties, only to discover that the babies had Down’s syndrome. One decided to have a termination. The other went through with the pregnancy, only to have her daughter die during labour.

Nature is cruel, and modern medicine doesn’t necessarily make it less so.

All it does is give us more choices, for which we then hold ourselves responsible. Even the treatments that are supposed to offer hope to the childless may prove to be a mixed blessing. Recent research suggests that the drug Clomid, which is often used to stimulate women’s ovaries, may be partly responsible for the higher rate of birth defects among children conceived through fertility treatments. One scientist, talking toThe New Republicearlier this year, described the drug as a “time bomb”.

Likewise, there is concern over a commonly used form of IVF known as ICSI (intracytoplasmic sperm injection), in which an individual sperm is injected into an extracted egg. Several studies have shown that ICSI produces higher rates of birth defects than any other treatment – perhaps because it removes the need for the sperm to find the egg and burrow into it, which only healthy sperm can do.

And yet, I take it back. Of course science has made nature more merciful – in ways so comprehensive that it is easy to take them for granted. The chances of dying in childbirth – still the leading cause of death among women in many parts of the world – are now minuscule here. Infant mortality rates are so low (0.46 per cent of babies under a year old) that the death of a child seems an unimaginable disaster, rather than the commonplace tragedy it once was.

Thanks to modern contraception we have fewer babies, but treasure them more. In 1900 – when no better form of family planning was available – the infant murder rate was 15 times what it is today. Seen in this light, the panic over older parents starts to look like a high-class problem.

Personally, I only have one serious regret about having my children late. My parents are in their seventies now, and starting to show signs of wear and tear. My father has cancer and a heart murmur. The anxiety I feel on my own behalf, as his daughter, is exacerbated by panic at the thought that my children might grow up without really knowing him. If he dies soon, will they remember him?

I want my children to have decades in which to know and love their grandparents, the way I did mine. And I want the experience of being a grandmother myself: not just a totemic one, dozing in a nursing home, but an active, involved figure in their lives.

At present, the odds are against me. A woman who has a baby at 35 is more likely than not to have died by the time that child is 46.

If my children follow my reproductive example – as children are wont to do – I will be dead before my first grandchild reaches 10.

It is possible, of course, that by then we will all be made of bionic spare parts and live to 1,000. I do hope so. If science can keep us fit and useful, the rise of the older parent may come to seem less scary. After all, we never meant to frighten anyone. We were just trying to live the fairy tale.